The Ransom Note may have been a device to cover-up or obscure the state of affairs that ensued after JonBenet's death.
The note refers to beheading not asphyxiation, there is repetition of "she dies", and if instructions are followed a "100% chance of getting her back", but she was dead!
Also she has head and genital injuries none of this is predicted or reflected in the Ransom Note.
So its likely the Ransom Note was concocted to explain away another scenario, one, which was later, revised then possibly tweaked as she was placed in the wine cellar.
The person who killed JonBenet may not be the same person who placed her in the wine cellar, or the person who wrote the Ransom Note. These are diversionary tactics not the methods of a foreign professional assassin.
The person who wrote the Ransom Note may be a sociopath guided by reference to theology and scripture. For example the use of cords and bindings, the knotting and vaginal trauma may reflect a desire for sadistic ritual. Also the letters SBTC can be interpreted as (S)aved (B)y (T)he (C)ross, psalm 118 is used charismatically within the Pentecostal movement, all can be utilized to project the Christian sense of Sacrifice. But it does not follow that the composer must have killed JonBenet! Only that this thumbnail psychological profile matches that of the author.
So the Ransom Note refers to another time, another place where JonBenet still lives, the concept of kidnap and bodily removal moves her temporal existence backwards in time and forward into the future only if instructions are followed. There is the deliberate promotion of JonBenet's presence, which is bogus and illusory.
The tone, structure and ambiguous semantics implied within the Ransom Note are patently not the work of a preteen or teen, it has adult persona all over it, and it has one purpose e.g. to mislead and misdirect the reader.
And to this end it has been largely successful!